1. Field of the Invention:
This invention relates generally to scanning force microscopes, and more particularly concerns a sensor module for a scanning force microscope with integrated scanning drivers for use with a stationary specimen.
2. Description of Related Art:
Scanning force microscopes, also known as atomic force microscopes, are useful for imaging objects as small as atoms. The scanning force microscope is closely related to the scanning tunneling microscope and the technique of stylus profilometry, however in a typical scanning force microscope, deflection of a laser beam by a vertical movement of a probe following the contours of a specimen is amplified by a reflective lever arm to which the probe is mounted. The deflection of the laser beam is typically monitored by a photodetector in the optical path of the deflected laser beam, and the sample is mounted on a stage moveable in minute distances in three dimensions so that the sample can be raster scanned while the vertical positioning of the probe relative to the surface of the sample is maintained substantially constant by a feedback loop with the photodetector controlling the vertical positioning of the sample.
Such scanning force microscopes are useful for imaging a sample which is moved in three dimensions while the sensor head is stationary and separate from the scanning assembly moving the sample. However, this conventional design is only useful for samples which are comparatively small or which can be cut small enough from a larger specimen to be examined on the scanning stage of the microscope. Such samples typically must also weigh about a gram or less, in order to accommodate the relatively high scan rates without causing distortion due to resonance effects. Although one design for a free standing scanning force microscope includes a scanning mechanism and sensor element for scanning large samples, the design is difficult to operate and employs a sensor head force on a sample which prohibits use of the microscope for scanning many polymers and biological molecules. It would therefore be desirable to provide an improved free standing scanning force microscope which can be used to examine the surface of minute samples and stationary samples of larger sizes, and weights greater than a gram, in principle without limitation.
It would also be desirable to provide a scanning force microscope with the capability of scanning a sample in contact with a fluid, without the preparation of special fluid cells or special adapters. This capability would be particularly useful in some applications, as such a fluid environment can significantly change scanning conditions and opportunities, and can improve the quality of the image of the sample developed by the instrument.
In conventional scanning force microscopes, a probe can also be damaged by too abrupt an approach to a sample before feedback position control of the sensor head is actually engaged. The user typically can not easily view the approach of the lever arm and probe assembly to the surface of the sample to insure precise positioning of the probe. Even where an optical microscope is used in conjunction with the scanning force microscope to view the sample, the arrangement of the optical microscope with the scanning force microscope can be inconvenient and clumsy, and can interfere with the operation of the scanning force microscope. It would further be desirable to provide the base of the microscope with motorized driver means for operating the approach of the optical lever arm and sensor head to the sample, which can be controlled by feedback control means, to allow the process of approach of the sensor head to the sample to be automated. The present invention meets these needs.